LIBRARY 

OF  THE 

UNIVERSITY  OF  CALIFORNIA. 


Class 


LABORATORY   NOTES 


ON 


HEAT    MEASUREMENTS 


BY 


CHARLES   L.   NORTON 


COPYRIGHT,    1902,    BY  CHARLES  L,   NORTON 


PRINTED      BY      THE      SOUTHGATE      PRESS 
T.     W.     RIPLEYCO.,     BOSTON,     U.S.  A, 


LABORATORY   NOTES 


ON 


HEAT    MEASUREMENTS 


BY 


CHARLES   L.    NORTON 


OF  THE 

UNIVERSITY 

OF 


COPYRIGHT,    1902,    BY  CHARLES  L.    NORTON 

PRINTED      BY      THE      SOUTHGATE      PRESS 
T.     W.     RIPLEYCO.,     BOSTON,      U.S.A. 


LABORATORY  OF  HEAT  MEASUREMENTS 

The  instruction  in  heat  measurement  consists  of  a  series  of 
lectures  and  laboratory  exercises  which  have  for  their  object 
the  training  of  the  student  in  such  methods  of  heat  and 
temperature  measurement  as  will  be  of  value  in  later  scien- 
tific or  technical  work,  and  to  furnish  a  foundation  for 
research  in  thermal  lines.  Perhaps  no  portion  of  the  heat 
measurement  field  is  so  fruitful,  both  to  the  scientific  and  to  the 
technical  investigator,  as  is  the  measurement  of  high  tem- 
peratures, or  pyrometry.  Next  in  importance  comes  the 
measurement  of  the  efficiency  of  fuels,  the  determination  of 
their  calorific  power.  To  these  two  subjects  the  first  portion 
of  these  laboratory  notes  is  devoted,  with  the  expectation 
that  the  additional  notes  on  "  thermometry,"  "  thermal  con- 
ductivity," and  "electric-heating  apparatus  and  methods" 
may  soon  be  added. 

All  reports  handed  in  must  be  taken  upon  the  proper 
blanks  and  Tegular  physical  laboratory  paper  and  should  be 
accompanied  by  the  original  records.  All  reports  must  be 
sent  in  within  two  weeks  of  the  time  the  observations  were 
finished.  When  sent  back  for  correction  they  should  be 
returned  with  all  necessary  corrections  within  one  week.  If 
not  returned  to  the  student  within  two  weeks  from  their  first 
presentation,  the  experiments  may  be  assumed  to  need  no 
correction,  and  they  will  not  be  returned  to  the  student  until 
the  end  of  the  term. 


THE  LE  CHATELIER  THERMO-ELECTRIC  PYROMETER 

The  Le  Chatelier  thermo-electric  pyrometer  is  based  upon 
the  increasing  electromotive  force  which  exists  at  a  junction 
of  two  metals  as  the  temperature  rises.  If  we  have  a  pair 
of  dissimilar  metallic  wires,  their  junction  becomes  the  seat 
of  an  electromotive  force,  and  if  they  be  joined  at  both 
ends,  a  current  will  flow  through  them  as  the  result  of  the 
difference  between  the  electromotive  forces  at  the  two  ends 
of  the  wires.  In  general,  this  current  is  dependent  upon  the 
difference  in  temperature,  though  not  directly  proportional 
to  it.  In  order  to  use  this  phenomena  as  a  basis  for  a 
pyrometer,  since  there  is  no  known  relation  existing  directly 
between  temperature  and  electromotive  force  in  such  a  cir- 
cuit, we  must  expose  the  junction  to  known  temperatures 
and  note  the  current  flowing,  and  in  this  way  calibrate.  It 
is  usually  customary  to  observe,  not  the  electromotive  force, 
but  the  current,  keeping  the  total  resistance  of  the  circuit 
constant  in  order  that  this  may  be  allowable. 

This  pyrometer  is  by  far  the  most  important  instrument 
for  the  measurement  of  temperature  from  the  point  of  view 
of  the  engineer.  It  may  be  found  described  in  detail  in 
Le  Chatelier's  "  High  Temperature  Measurements,"  pages 
92  to  128  (Burgess  translation). 

The  apparatus  consists  :  first,  of  a  pair  of  platinum  and 
platinum-iridium  wires;  second,  of  a  galvanometer;  ana 
third,  a  pair  of  suitable  connecting  leads. 

Leads.  —  The  lead  wires  connecting  the  galvanometer  to 
the  junction  do  not  require  any  special  care,  other  than  that 
necessary  to  keep  them  well  insulated.  These  wires  should 
be  of  seme  good  electric  line-wire,  not  smaller  than  No.  14, 
and  they  should  preferably  be  of  the  so-called  "  rubber-cov- 
ered "  type. 


LABORATORY  OF  HEAT  MEASUREMENTS 


Junction.  —  The  junction  to  be  used  is  composed  of  one 
wire  of  platinum,  and  one  of  platinum  with  ten  per  cent,  of 
rhodium  or  iridium.  This  couple  costs  nearly  ten  dollars  a 
foot  and  must  be  used  with  great  care.  The  wires  are  some- 
what brittle,  and  they  are  easily  attacked  when  hot  by  many 
of  the  baser  metals.  The  junction  in  its  simplest  form  is 
made  by  merely  twisting  the  wires  together  at  one  end  and 
then  twisting  each  to  the  leads  at  the  other  end.  It  is  desir- 
able, however,  to  be  able  to  know  the  temperature  of  the 
junction  of  the  couple  with  the  copper  leads,  and  it  is  there- 
fore best  to  inclose  the  joints  in  some  receptacle  in  which  a 
thermometer  bulb  can  be  inserted.  For  laboratory  work,  a 


FIG.    I .  —  Diagram  of  Thermal  Couple. 

small  bottle  with  a  stopper  perforated  for  the  leads  and  ther- 
mometer serves  to  keep  the  junction  at  a  fairly  even  temper- 
ature. Where  greater  constancy  of  temperature  is  needed 
the  bottle  may  be  wrapped  with  some  insulating  material, 
felt,  magnesia,  or  asbestos.  It  is  sometimes  necessary  to 
put  the  "cold  junction,"  as  the  copper-platinum  end  of  the 
couple  is  called,  in  a  large  block  of  iron  to  insure  its  chang- 
ing temperature  only  at  a  very  gradual  rate. 

The  couple  must  be  insulated  from  itself  and  from  sur- 
rounding conductors  throughout  its  length.  The  best  insula- 
tion for  the  cool  portions  of  the  wires  is  a  firre  rubber  tube, 
while  the  hotter  portions  may  be  insulated  with  asbestos 
string  wound  over  and  under,  in  figure-eight  fashion,  or  they 
may  be  protected  by  means  of  small  clay  stems  with  a 
double  bore. 


THERMO-ELECTRIC    PYROMETER  5 

To  insure  a  constant  resistance  of  the  couple  and  leads  it 
is,  in  all  cases,  best  to  solder  the  cold  junction  with  ordinary 
soft  solder.  Resin,  and  not  acid,  should  be  used  in  fluxing 
this  joint,  or  a  slight  electromotive  force  will  be  found 
to  result,  giving  serious  disturbance  to  the  galvanometer 
readings. 

Unless  there  is  a  switch  on  the  galvanometer  there 
should  be  one  inserted  in  the  circuit,  as  it  is  necessary  to 
open  the  circuit  frequently  for  the  purpose  of  reading  the 
zero. 

Galvanometers.  —  There  are  many  galvanometers  suitable 
for  use  with  a  thermal  couple.  Directions  will  be  given  for 
the  adjustment  and  operation  of  those  now  in  use  in  the 
Laboratory  of  Heat  Measurements,  and  since  the  galva- 
nometers are  of  the  same  general  class  it  is  probable  that  no 
great  difficulty  will  be  found  in  applying  them  to  others. 
All  the  galvanometers  especially  suited  for  this  work  are  of 
the  D'Arsonyal  type,  of  medium  sensitiveness.  They  oper- 
ate by  the  change  in  position  of  a  coil  of  wire  in  a  magnetic 
field,  as  the  current  in  the  coil  changes  in  strength.  This 
change  in  position  is  noted  either  by  observing  the  move- 
ment of  a  pointer  attached  directly  to  the  coil,  or  by  noting 
the  excursion  of  a  beam  of  light  falling  upon  a  small  mirror 
attached  to  the  movable  coil.  Galvanometers  which  may  be 
read  by  a  pointer  are  made  by  Heraeus,  and  Hartmann  and 
Braun.  The  galvanometers  of  Sullivan  and  Carpentier  are 
the  best  of  the  instruments  using  a  mirror  and  scale.  The 
more  important  details  of  the  procedure  in  setting  up  each  of 
these  instruments  are  given  below. 

Carpentier  galvanometer.  —  This  instrument  is  that  most 
commonly  adopted  for  pyrometric  determinations.  It  will 
be  found  described  in  Le  Chatelier,  pages  108  to  no.  To  set 
up  the  galvanometer  one  should  select  a  place  as  free  from 
vibration  as  possible,  and  screen  it  from  any  but  a  feeble 
light.  -  The  galvanometer  box  should  be  firmly  attached  to 
the  wall,  taking  care  to  see  that  it  is  plumb.  The  small  bob 
inside  the  box  is  intended  to  assist  this  operation.  Next 
slip  the  coil  over  the  iron  block  between  the  pole  pieces,  with 


6          LABORATORY  OF  HEAT  MEASUREMENTS 

its  mirror  facing  in  the  direction  in  which  the  lamp  and  scale 
is  to  be  placed.  The  suspensions  consist  of  short  pieces  of 
fine  German  silver  wire  with  little  balls  of  the  same  metal 
wedged  on  to  the  ends.  The  lower  end  of  the  upper  sus- 
pension should  first  be  inserted  in  its  eye  at  the  top  of  the 
coil.  See  that  it  is  slipped  well  back  in  the  slot.  Next 
hook  the  upper  end  of  the  suspension  in  the  eye  in  the  flat 
spring  near  the  top  of  the  box.  If  the  suspension  is  appar- 
ently too  short  loosen  the  tension  of  the  flat  spring  by  means 
of  the  thumb-screw.  Next  drop  the  lower  suspension  into 


FIG.    2.  —  Carpentier  Galvanometer. 


place  in  the  opening  between  the  magnets,  and  put  its  two 
ends  in  the  eyes  as  before.  The  mirror  may  now  be  made 
to  face  in  any  desired  direction  by  taking  the  ball  at  the 
lower  end  of  the  lower  suspension  between  the  thumb  and 
finger  and  twisting  it  slightly.  This  is  the  most  troublesome 
operation  of  the  whole  process,  and  must,  moreover,  be 
accompanied  with  the  exercise  of  great  care  and  patience, 
or  the  only  result  of  a  great  expenditure  of  time  will  be  a 
pair  of  broken  suspensions.  A  small  amount  of  adjustment 
of  the  light  spot  may  be  gotten  later  by  means  of  the  screw- 
feet  at  the  bottom  of  the  box. 

The  lamp  and  scale  should  next  be  set  up  at  a  distance  of 
about  a  meter.     It  is  well  to  light  the  lamp  and  move  it  back 


THERMO-ELECTRIC    PYROMETER  / 

and  forth,  and  up  and  down,  until  it  is  found  that  the  image 
is  well  focussed,  and  at  such  a  height  as  makes  both  the 
divisions  and  numbers  of  the  scale  visible.  When  its  proper 
position  is  found  the  base-board  should  be  firmly  fastened  to 
the  wall.  It  is  well  to  put  in  a  strong  screw  at  the  middle  of 
the  board  near  the  bottom,  in  addition  to  the  screwr  at  the 
top.  The  oil  lamp  which  is  often  used  where  the  apparatus 
is  to  be  carried  about,  often  covers  the  lens  with  dew  for  a 
few  minutes  after  lighting,  and  it  is  well  to  put  off  any 
attempts  at  focussing  until  this  has  disappeared,  after  the 
whole  lantern  becomes  warm.  As  this  lamp  requires  refilling 
at  very  short  intervals,  it  should  be  used  only  when  absolutely 
necessary.  Either  a  small  gas  burner  or  an  incandescent 
lamp  .should  be  used  whenever  possible. 

Heraeus  galvanometer.  —  This  galvanometer  reads  by 
means  of  a  pointer  attached  directly  to  the  coil.  The  coil 
must  therefore  move  through  a  much  larger  angle  than  in 
the  case  of  the.Carpentier  instrument  with  its  long  beam  of 
light.  To  make  the  galvanometer  sufficiently  sensitive  to 
accomplish  this,  it  has  been  necessary  to  use  a  very  fine 
suspension  wire,  and  to  use  only  the  upper  suspension.  The 
galvanometer  is  therefore  more  frail  and  must  be  handled 
with  great  care.  There  are  only  two  adjustments  neces- 
sary :  first,  level  by  means  of  the  screw-feet  and  the  circular 
level  attached  to  the  base ;  and  second,  loosen  the  brass 
thumb-screw  which  projects  through  the  side  of  the  brass 
case.  This  removes  the  supporting  spring  which  lifts  the 
coil  and  takes  all  strain  from  the  suspension.  It  is  abso- 
lutely necessary  to  screw  this  thumb-screw  firmly  in,  before 
attempting  to  move  the  galvanometer,  otherwise  the  suspen- 
sion is  quite  certain  to  be  broken.  There  are  two  scales 
upon  the  dial.  The  outer  scale  is  intended  to  read  in  Centi- 
grade degrees  directly,  with  an  upper  limit  of  1600°.  The 
lower  scale  is  in  millivolts  and  it  is  intended  to  make  the 
instrument  thereby  available  as  a  voltmeter  as  well  as  a 
pyrometer.  In  several  of  the  later  galvanometers  of  this 
kind  there  is  noticeable  considerable  "  pivot  friction,"  mak- 
ing it  necessary  to  tap  the  glass  of  the  galvanometer  contin- 


8          LABORATORY  OF  HEAT  MEASUREMENTS 

ually  to  be  sure  of  freedom  from  error  due  to  the  pivo* 
sticking.  None  of  the  joints  in  these  galvanometers  in  the 
laboratory  were  soldered  when  they  were  purchased,  and 
their  variations  in  resistance  made  it  necessary  to  solde* 
most  of  them. 

Sullivan  galvanometer*  —  This  galvanometer  is  similar  in 
many  respects  to  that  of  Carpentier.  It  reads  by  means  ot 
a  mirror  and  has  an  upper  and  lower  suspension.  It  is. 
however,  more  sensitive  and  it  is  so  free  from  disturbance 
from  jarring  that  it  may  be  satisfactorily  used  on  an  ordinary- 
laboratory  table.  Further,  the  suspension  is  stout  enough  to 
allow  the  galvanometer  to  be  readily  handled  and  shipped 
without  any  unusual  care.  As  set  up  in  the  laboratory,  it  is 
to  be  used  with  a  telescope  and  scale.  The  scale  must  first  be 
set  up  in  front  of  the  galvanometer  at  a  distance  of  about  a 
meter.  The  telescope  should  be  focussed  on  the  plane  mir- 
ror and  then  gradually  refocussed  until  the  image  of  the 
number  on  the  scale  can  be  clearly  seen.  Some  care  is 
needed  in  placing  the  scale  and  telescope  at  the  proper 
height,  and  also  in  a  plane  perpendicular  to  the  axis  on 
which  the  coil  turns,  so  that  the  image  may  remain  in  the 
field  of  view  as  the  mirror  turns.  Care  must  be  used  not  to 
disturb  the  focus  of  the  telescope  after  calibrating,  as  the 
axis  of  the  telescope  is  not  sufficiently  constant  in  position  to 
allow  of  even  slight  adjustments,  without  altering  the  appar- 
ent position  of  the  cross  hairs. 

Calibration.  —  Having  prepared  the  junction  and  having 
gotten  the  galvanometer  set  up  and  attached  to  the  leads 
through  the  switch,  the  galvanometer  may  now  be  cali- 
brated. To  do  this  we  observe  the  deflection  of  the  gal- 
vanometer which  corresponds  to  a  known  difference  of 
temperature  at  the  two  ends  of  the  thermal  junction.  The 
most  convenient  temperatures  to  use  are  the  boiling  and 
melting  points  given  below.  The  cold  junction  may  be 
placed  in  a  steam  or  ice  bath,  when  desired,  but  it  is  usually 
sufficient  to  allow  it  to  remain  at  the  temperature  of  the 
room  and  read  its  thermometer  at  intervals  of  two  to  five 
minutes. 


THERMO-ELECTRIC    PYROMETER  9 

TEMPERATURES    FOR    CALIBRATION 

Substance.  Boiling  Point.  Freezing  Point. 

Water  ioo.°  C.  o°.  C. 

Naphthaline  218.° 

Sulphur  444. 

Aluminum  657. 

Copper  1084. 

Gold  1063. 

Platinum  1760. 

The  hot  junction  should  be  exposed  to  these  several  known 
temperatures  while  the  deflection  of  the  galvanometer  and 
the  temperature  of  the  cold  junction  are  noted,  in  each 
instance.  A  plot  should  then  be  made  having  the  deflections 
as  ordinates  and  the  difference  between  the  temperature  of 
the  hot  and  the  cold  ends  of  the  couple  as  abscissas.  If  the 
Heraeus  galvanometer  is  to  be  used  with  a  couple  of  compo- 
sition similar  to  that  for  which  it  was  originally  graduated, 
it  may  be  well  to  make  the  plot  as  a  plot  of  corrections,  hav- 
ing readings  of  the  instrument  as  abscissas  and  corrections  as 
ordinates. 

To  obtain  the  galvanometer  readings  corresponding  to  the 
boiling  points  of  water,  napthaline  and  sulphur,  it  is  best  to 
put  the  junction  directly  into  a  small  test  tube  of  the  boiling 
liquid.  It  makes  no  difference  whether  the  junction  be  just 
above  the  liquid  or  well  below  the  surface.  Take  care  not 
to  heat  so  vigorously  as  to  superheat,  or  to  cause  the  vapors 
to  catch  fire  at  the  mouth  of  the  tube.  The  highest  steady 
deflection  is,  of  course,  the  one  to  be  recorded. 

To  find  the  deflection  corresponding  to  the  freezing  points 
of  the  metals,  we  may  use  either  a  small  bit  of  the  metal 
wrapped  about  the  hot  junction  or  a  larger  mass  in  a  crucible. 
To  heat  the  smaller  mass,  it  is  only  necessary  to  use  a  Bunsen 
burner  for  the  baser  metals  and  an  oxyhydrogen  blow-pipe 
for  the  platinum.  For  the  larger  masses,  a  crucible  furnace, 
similar  to  the  small  Fletcher  furnaces  in  the  laboratory,  will 
be  needed.  The  metal  should  in  all  cases  be  heated  slowly, 
and  the  greatest  care  should  be  used  to  prevent  heating  more 


10         LABORATORY  OF  HEAT  MEASUREMENTS 

than  a  very  few  degrees  above  the  melting  point,  as  otherwise 
the  platinum  and  platinum-rhodium  will  alloy  with  the  melted 
metal,  changing  its  composition  and  its  freezing  point,  and 
the  loss  of  a  portion  of  the  junction  is  also  very  probable. 
Especial  care  is  needed  when  working  with  hot  copper,  as 
the  fumes  or  vapor  arising  from  the  melted  metal,  if  it  be 
heated  much  above  its  melting  point,  cause  the  platinum  to 
be  alloyed  at  a  distance  of  an  inch  or  two  from  the  surface 
of  the  hot  copper.  Since  it  is  difficult  to  tell  from  its  physi- 
cal condition,  even  when  large  masses  are  used,  at  just 
what  temperature  a  metal  melts  or  freezes,  it  is  best  to 
use  the  point  at  which  the  latent  heat  of  freezing  develops 
as  the  freezing  point.  To  do  this  it  is  only  necessary  to 
note  the  point  at  which  the  galvanometer  pauses  in  its 
swing  as  the  melted  metal  cools.  This  momentary  pause 
occurs  when  the  latent  heat  of  freezing  develops  and  pre- 
vents for  a  brief  interval  the  temperature  of  the  mass  from 
passing  below  the  freezing  point  until  all  the  metal  has 
frozen.  To  find  the  platinum  point  it  is  best  to  use  a  long 
flame  from  an  oxyhydrogen  blow-pipe  and  draw  the  junction 
slowly  down  through  it  until  the  platinum  wire  melts.  With 
care,  a  drop  of  melted  platinum  may  be  kept  on  the  tip  of 
the  wire  for  several  seconds,  and  the  deflection  can  be  read 
with  a  precision  quite  as  good  as  in  the  case  of  the  other 
metals.  The  eyes  must  be  protected  from  the  intensely 
bright  light  of  the  melted  metal  by  very  dark  glasses,  such 
as  are  used  in  examination  of  the  electric  arc.  The  junction 
wires  may  be  protected  from  alloying  with  metals  of  low 
melting  points  by  a  fine  hard  glass  tube,  but  in  case  this  is 
done,  larger  masses  of  metal  must  be  used  to  insure  the 
junction  being  at  the  temperature  of  the  melted  metal. 

Reports.  —  Each  pair  of  students  will  be  expected  to  set 
up  their  galvanometer  and  calibrate  it,  possibly  omitting  the 
platinum  point  from  motives  of  economy.  They  will  next 
measure  several  unknown  temperatures,  preferably  the  recal- 
escence  points  of  two  pieces  of  steel,  and  the  melting  points 
of  several  alloys.  In  case  antimony  is  used  it  is  necessary 
to  perform  the  melting  point  determination  under  the  hood. 


PLATINUM    RESISTANCE    PYROMETER  II 

After  having  gotten  the  deflections  corresponding  to  the  points 
sought,  they  should  be  looked  up  in  the  calibration  plot,  not 
forgetting  the  necessary  addition  of  the  cold  junction  tem- 
perature. Bear  in  mind  that  the  deflection  is  dependent 
upon,  not  the  temperature  of  the  hot  junction,  but  the  differ- 
ence in  temperature  between  the  hot  and  cold  ends. 

PLATINUM    RESISTANCE   PYROMETER 

The  platinum  resistance  pyrometer,  or  thermometer,  of 
Siemens  and  Callendar  may  be  found  described  in  Le  Chat- 
elier,  pages  83  to  91.  It  is  not  always  given  place  among 
the  pyrometers,  nowadays,  because  of  the  great  difficulty  of 
keeping  the  apparatus  in  proper  condition  if  used  at  tem- 
peratures much  above  500°  C.  Since,  however,  its  preci- 
sion is  very  great  at  low  temperatures,  and,  further,  since 
in  the  hands  of  some  exceptional  observers  it  has  yielded 
excellent  results,  it  should  be  classed  as  one  of  the  most 
important  thermometers. 

The  operation  of  the  pyrometer  is  based  upon  the  increase 
of  the  electrical  resistance  of  a  platinum  wire  as  its  tempera- 
ture rises.  After  calibration  we  have  only  to  measure  the 
resistance  of  the  wire  in  order  to  determine  its  temperature. 
It  will  be  apparent  at  once  that  the  method  is  available  for 
use  at  great  distance  and  under  varying  conditions  of  pres- 
sure, and  in  many  ways  offers  advantages  over  most  other 
methods.  Since  it  is  not  difficult  to  measure  the  resistance  of 
such  a  coil  as  may  easily  be  used  in  this  work  with  a  pre- 
cision of  one-twentieth  of  one  per  cent.,  the  method  takes 
first  place  in  the  ranks  of  the  thermometers  in  the  matter  of 
precision. 

The  essential  parts  of  the  apparatus  are,  of  course,  a  coil  of 
platinum  wire  and  a  bridge  with  which  to  measure  its  resis- 
tance. Since  the  adjustment  and  subsequent  care  of  a  gal- 
vanometer and  Wheatstone's  bridge  of  the  greatest  precision 
would  be  so  great  as  to  call  for  a  considerable  outlay  of  time, 
it  is  deemed  best  to  use  a  less  sensitive  measuring  device 
and  devote  more  time  to  studying  the  method  of  using  and 


12         LABORATORY  OF  HEAT  MEASUREMENTS 

calibrating  the  pyrometer.  Students  will  therefore  use  either 
the  portable  testing  set  or  a  similar  simple  bridge  with  a 
D'Arsonval  galvanometer.  The  greatest  precision  sought 
is  a  single  degree.  Be  sure  and  note  the  number  of  the  coil 
used. 

Connect  up  the  apparatus  and  measure  the  resistance  of 
the  coil  at  the  room  temperature.  The  blind  leads  may 
either  be  connected  in  the  opposite  side  of  the  bridge  circuit, 
or  they  may  be  measured  separately  and  subtracted.  Of 
course  the  object  of  this  is  to  enable  us  to  measure  the 
resistance  of  the  coil  alone  without  the  leads,  and  it  is  for 
that  purpose  that  the  blind  leads  are  inserted.  They  are 
of  the  same  wire  and  length  as  the  true  leads,  and  their 
position  beside  the  true  leads  assures  their  being  at  the  same 
temperature.  Find  the  resistance  of  the  coil  in  ice,  in  steam, 
in  boiling  sulphur,  and  in  boiling  napthaline.  Take  great 
care  to  keep  the  tube  which  protects  the  coil  from  too  sud- 
den changes  in  temperature,  as  its  breaking  may  cause  the 
.breaking  of  the  platinum  coil,  a  rather  serious  matter,  as 
these  coils  are  difficult  to  wind.  Having  found  the  resis- 
tances, compute  first  the  "platinum  temperature"  -pi  for 
boiling  sulphur.  This  temperature  will  be  found  to  be  some 
ten  or  twenty  degrees  below  the  true  boiling  point  as  ex- 
pressed in  degrees  centigrade  (444°).  The  formula  for  this 
deduction  is 

7P       /? 

IOQ       f~  —  -j-—pt  (in  platinum  degrees). 

^100  —  J?o 

To  reduce  the  pt  in  platinum  degrees  to  degrees  centigrade 
we  must  make  use  of  Callendar's  second  formula,  in  which  / 
is  the  temperature  in  degrees  centigrade  and  pt  the  platinum 
temperature  as  found  under  the  assumption  of  the  equation 
above,  that  the  increase  of  resistance  is  directly  proportional 
to  the  temperature  increase. 


In  this  equation  we  may  substitute  the  values  of  pt  and  /  for 
the  sulphur  point  and  solve  for  D.     This  need  not  be  rede- 


CALORIMETRIC    PYROMETER  1 3 

termined  so  long  as  the  coil  remains  free  from  injury  or 
contamination  chemically.  Next,  with  the  aid  of  the  first 
formula,  find  the  platinum  temperature  of  the  boiling  naph- 
thaline, and  then  substitute  in  the  second  formula,  and  find 
the  boiling-point  in  centigrade  degrees.  The  values  of  /  are 
of  course  not  known  in  the  substitution  in  the  second  formula 
and  -pt  may  be  substituted  instead  for  a  first  approximation. 
A  second  substitution  should  then  be  made  with  the  values 
thus  found.  This  second  approximation  will  be  sufficiently 
precise.  Take  care  to  leave  the  apparatus  in  the  condition 
in  which  it  was  found,  especially  taking  care  to  cut  off  all 
the  gas  and  electrical  supply  from  the  boiling-point  cans. 

CALORIMETRIC    PYROMETER 

The  calorimetric  pyrometer,  or,  as  it  is  often  called,  the 
specific  heat  pyrometer,  of  Siemens  and  Violle  may  be  found 
described  on  pages  74  to  82  of  Le  Chatelier.  The  measure- 
ment of  a  temperature  by  the  calorimetric  method  involves 
the  measurement  of  the  heat  given  out  by  the  pyrometric 
substance  in  cooling  from  the  unknown  temperature  to  the 
temperature  of  the  calorimeter  in  which  it  is  plunged.  If  we 
know  the  specific  heat  and  weight  of  the  substance,  we  may 
compute  the  temperature,  from  the  total  heat  received  by 
the  calorimeter.  Unfortunately  the  specific  heat  of  such 
substances  as  are  available  for  pyrometry  varies  rapidly  with 
the  temperature. 

Let  W=  weight  of  the  substance  (platinum  or  nickel  ball). 
w  =  weight  of  water  in  the  calorimeter. 
5  =  the  specific  heat  of  the  calorimeter  and  stirrer. 
t°  =  initial  temperature  of  the  calorimeter. 
/2°  =  final  temperature  of  the  calorimeter. 
T°  == ;  unknown  temperature  to  be  measured. 
sr  =  mean  specific  heat  of  pyrometric  substance  (o°  to 
st  =  specific  heat  of  pyrometric  substance  (o°  to  /2°). 
c  =  weight  of  the  calorimeter  and  stirrer. 


14          LABORATORY  OF  HEAT  MEASUREMENTS 

Then  when  the  substance  is  taken  from  the  furnace,  and  is 
plunged  into  the  calorimeter  whose  temperature  thereupon 
rises  from  t,  to  t2  the  transfer  of  heat  is  shown  by  the  fol- 
lowing equation  : 


WTsT  -   Ws,i,  =  (t,  _  /,)  (TV  +  cs) 
and  7W^><T  +  -W 

All  the  terms  in  the  right-hand  member  of  this  equation 
are  known  after  the  transfer  and  subsequent  rise  of  temper- 
ature. The  term  at  the  left  TsT  is  the  total  heat  given  out 
by  one  gram  of  the  substance  in  cooling  from  T°  to  o°. 
This  quantity  has  been  very  carefully  determined  for  platinum 
and  nickel  by  Violle  and  others.  The  values  for  platinum  are 
given  in  the  table  below,  for  temperatures  over  a  wide  range. 

T  TsT 

100°    ..........       3.23  cal. 

200     ..........       6.58 

300     ..........       9-75 

400     ..     ........     13.64 

5°°  ........     -     •  J7-35 

600  ..........  21.  18 

700  ..........  25.13 

800  ......     ....  29.20 

9°o     .........     •     33-39 

1000     ..........     37.70 

noo     ..........     42-I3 

1200     ..........     46.65 


14°°     ..........  56-J4 

1500     ..........  61.05 

1600     ..........  66.08 

1700     .....     .....  71.23 

1800     ..........  76.50 

Having  computed  the  value  of  the  left-hand  member  of  the 
equation  by  substituting  the  numerical  values,  the  value  of  T 


CALORIMETRIC    PYROMETER  1 5 

may  be  found  by  interpolating  between  the  values  of  TsT  in 
the  tables. 

Apparatus  for  temperature  measurement  in  this  way  is  of 
all  degrees  of  refinement,  from  an  old  tin  can  and  a  bit  of 
firebrick  and    an  ordinary  house  thermometer,  to  the  care 
fully  jacketed  calorimeter  for  use  with  the  platinum  ball  in 
the  laboratory.     There  is  no  other  method  which  can  be  used 


FIG.    3.  —  Calorimetric   Pyrometer. 

with  so  little  initial  cost,  nor  so  available  in  regions  where 
little  apparatus  is  to  be  had.  The  precautions  to  be  observed 
are  the  following  : —  If  iron  is  used  for  the  ball  it  must  be 
weighed  each  time,  as  the  scale  which  forms  is  of  consid- 
erable weight.  It  is  not  best  to  use  iron  for  any  but  rough 
work.  The  water  in  the  calorimeter  should  be  of  such 
amount  as  to  give  a  rise  of  temperature  of  about  five  degrees, 
as  the  calorimeter  thermometers  are  to  be  read  to  -rW«  The 
water  at  the  start  should  be  five  or  six  degrees  below  the  tem- 
perature of  the  room.  Vigorous  stirring  is  necessary.  The 


l6         LABORATORY  OF  HEAT  MEASUREMENTS 

tongs  with  which  the  ball  is  taken  from  the  furnace  should 
be  heated  to  a  temperature  as  near  as  possible  that  of  the 
ball,  so  that  the  ball  may  not  be  unnecessarily  cooled  on 
being  grasped.  Use  all  possible  speed  in  making  the  transfer 
to  the  calorimeter,  as  the  ball  cools  very  rapidly  by  radi- 
ation in  even  a  very  few  seconds.  A  i5o-gram  ball  of  nickel 
or  platinum  should  be  allowed  to  remain  in  the  furnace  at 
least  twenty  minutes  before  attempting  to  use  it  to  measure 
the  temperature,  as  it  is  slow  in  arriving  at  the  exact  tem- 
perature of  the  furnace. 

Each  student  will  make  a  measurement  with  this  instru- 
ment of  the  temperature  of  melting  sodium  chloride,  and 
such  other  points  as  the  instructor  may  call  for.  The 
nickel  and  platinum  balls  or  cylinders  are  to  be  returned  to 
the  instructor  after  using.  Great  care  must  be  taken  to 
avoid  contact  of  the  platinum  with  hot  firebrick  or  other 
material  which  would  alter  its  chemical  purity.  The  ball 
must  always  be  heated  on  a  small  platinum  tripod  or  a  little 
pan  made  of  stout  platinum  foil.  In  order  that  the  ball  may 
not  be  further  contaminated  by  alloying  with  the  metal  of 
the  calorimeter,  a  net  of  platinum  wire  is  suspended  in  the 
water  of  the  calorimeter.  Failure  to  properly  care  for  the 
platinum  ball  when  in  use  may  lead  to  a  very  consider- 
able and  wholly  unnecessary  expense.  The  calorimeter  is 
mounted  on  wheels,  to  permit  of  its  being  drawn  very  near 
the  furnace  and  quickly  removed,  so  that  the  transfer  of 
the  ball  may  be  made  rapidly,  and  yet  the  calorimeter  need 
be  exposed  to  radiation  from  the  furnace  for  only  a  short 
time. 

To  measure  temperatures  of  about  one  thousand  degrees 
with  a  platinum  ball  weighing  one  hundred  and  twenty-five 
grams,  we  need,  if  we  wish  to  have  a  temperature  rise  of  five 
degrees,  500  to  900  grams  of  water  as  deduced  below. 
125  x  37-7°  =  5  x  W, 
W  —  940  grams  approx. 

This,  of  course,  makes  no  allowance  for  the  weight  of  the 
calorimeter,  and  this  need  not  usually  be  considered  in 


LE  CHATELIER  PHOTOMETRIC  PYROMETER        Ij 

estimating  the  amount  of  water  needed.  We  may  then  use 
from  five  to  nine  hundred  grams  of  water,  and  get  a  rise  in 
temperature  of  from  five  to  ten  degrees. 

The  only  advantage  of  using  distilled  water  for  this  work 
is  that  it  is  possible  to  keep  the  calorimeters  and  thermom- 
eters much  cleaner  when  it  is  used.  The  apparatus  is  to  be 
left  in  the  condition  in  which  it  was  found,  with  the  current 
for  the  motor  cut  off.  The  thermometers  are  to  be  returned 
to  their  rack,  and,  as  was  earlier  noted,  the  platinum  ball  is 
to  be  returned  to  the  instructor. 

LE   CHATELIER    PHOTOMETRIC    PYROMETER 

This  instrument  may  be  found  described  in  detail  in 
Le  Chatelier,  pages  144  to  148.  It  is  a  portable  photometer 
for  the  measurement  of  the  intensity  of  the  red  light  given 
out  by  a  hot  body.  When  a  body  is  heated  it  becomes  first  a 
dull  red,  and  then  a  brighter  red,  then  yellow,  and  finally 
white.  The  eye  does  not  indicate  that  as  the  temperature 
rises  the  intensity  of  the  red  increases,  because  the  increase 
of  other  colors  is  greater,  but  it  has  been  found  that  the 
increase  of  the  intensity  of  the  red  radiations  bears  a  certain 
definite  relation  to  the  temperature  increase.  Red  is  selected 
because  it  is  present  in  measurable  quantities  at  lower  tem- 
peratures. For  high  temperatures  it  would  be  quite  possible 
to  use  yellow  or  blue  light.  By  this  method,  then,  we  are  to 
measure  the  temperature  by  measuring  the  intensity  of  the 
red  light  given  out  by  the  body  whose  temperature  we  are 
seeking.  The  nature  of  the  surface  of  the  body  determines 
to  a  considerable  extent  the  amount  of  light  which  will  be 
radiated  from  it  when  it  is  raised  to  a  certain  temperature, 
but  as  this  instrument  is  essentially  a  secondary  one,  which 
must  of  necessity  be  calibrated,  it  is  only  necessary  to  cali- 
brate it  upon  some  surface  which  may  be  later  used  as  the 
surface  whose  brilliancy  is  measured  and  under  the  same  con- 
ditions as  prevail  in  its  later  use.  A  small  piece  of  platinum, 
or  a  bit  of  refractory  clay  will  answer  for  this  purpose. 

The  photometer  itself  is  of  the  Cornu  type,  and  it  is  shown 


i8 


LABORATORY    OF    HEAT    MEASUREMENTS 


in  plan  and  perspective  in  the  accompanying  cuts.  There 
are  two  telescopes  so  arranged  that  we  may  see  on  looking 
into  the  common  eyepiece,  as  if  side  by  side,  the  standard 
lamp  and  the  object  whose  temperature  is  sought.  Then 
by  means  of  the  diaphragm  in  the  direct  telescope  we  grad- 
ually diminish  the  apparent  brilliancy  of  the  object  until 
it  just  matches  in  intensity  the  standard  lamp.  The  amount 
of  '<  stopping  down "  necessary  to  make  the  two  images 
match  in  brilliancy  is  dependent  upon,  and  a  measure  of,  the 
temperature  of  the  hot  body.  In  other  words,  the  hotter  the 


FJG.   4.  —  Le  Chatelier  Photometric    Pyrometer. 

body,   the   more   we   must   close  the  diaphragm  in   order  to 
make  the  two  images  appear  of  the  same  intensity. 

The  instrument  as  shown  in  perspective  in  figure  4  and  in 
plan  in  figure  5  consists  of  the  telescope  71  with  the  eye- 
piece E,  the  bent  telescope  Tz  with  the  mirror  M  so  placed 
as  to  bring  its  objective  in  line  with  the  eyepiece  E;  the 
standard  lamp  S,  and  the  *  *  cat's-eye "  C.  The  arm  W 
carries  a  counterweight  to  make  the  apparatus  more  stable. 
Usually  the  standard  lamp  used  for  this  instrument  is  a  small 
kerosene  lamp.  This  is  a  source  of  great  inconvenience,  and 
moreover  its  variations  in  brilliancy  are  considerable.  It 
should  be  replaced  whenever  possible  by  an  Argand  burner 
or  a  large  kerosene  lamp,  having  a  flame  not  less  than  30 


LE  CHATELIER  PHOTOMETRIC  PYROMETER        Ip 

millimeters  in  height  or  breadth.  This  will  give  a  standard 
which  should  be  constant  in  intensity  within  about  two  per 
cent.  The  mirror  M  which  deflects  the  beam  of  light  from 
the  lamp  into  the  eyepiece  is  of  black  glass  with  an  exceed- 
ingly keen  edge,  so  that  the  two  images  may  appear  to  be 
in  close  contact  with  no  dark  line  between.  If  the  mirror 
should  become  displaced,  so  that  a  dark  line  appears  between 
the  images,  the  instructor  should  be  called  upon  to  readjust 
it.  The  eyepiece  E  needs  no  adjustment  nor  any  special 
mention,  except  that  it  is  liable  to  become  coated  with  dust 


FIG.    5. — Section  of  Photometer. 

and  will  need  frequent  cleaning.  This  applies  as  well  to  the 
objectives.  The  cat's-eye  C  has  a  scale  attached  which 
indicates  the  amount  of  the  travel  of  the  diaphragm  in  clos- 
ing or  opening.  It  should  be  in  such  adjustment  as  to  read 
zero  when  the  cat's-eye  is  closed.  The  telescope  T2  needs 
no  focussing  but  Tr  must  be  carefully  focussed  upon  the 
object  under  examination.  This  is  accomplished  by  sliding 
the  telescope  tube  in  or  out  after  loosening  the  small  set 
screw  on  the  top.  Since  there  is  some  uncertainty  as  to 
effect -upon  the  intensity,  as  measured  by  this  particular 
instrument,  of  light  coming  from  bodies  at  different  distances, 
it  is  best  to  calibrate  the  instrument  at  the  same  distance  as 
that  at  which  it  is  to  be  used. 


2O          LABORATORY  OF  HEAT  MEASUREMENTS 

One  or  two  meters  may  be  selected  as  a  convenient  distance 
for  the  laboratory. 

Having  gotten  the  instrument  together,  and  pointed  it  at 
the  small  furnace  which  is  to  be  used  to  heat  the  calibrating 
surface,  the  standard  lamp  should  be  lighted  and  the  tele- 
scope focussed.  This  can  be  best  done  when  the  cat's-eye 
is  wide  open.  If  the  furnace  is  not  yet  red  hot,  a  match  flame 
may  be  held  near  the  furnace  to  focus  upon.  It  is  well  to 
let  the  lamp  burn  for  some  minutes  before  beginning  the 
observations,  in  order  that  the  lamp  may  become  heated  and 
burn  at  its  normal  brilliancy.  The  telescope  should  next  be 
directed  toward  the  piece  of  platinum  in  the  furnace  which  is 
to  be  used  to  calibrate  with.  This  platinum  is  carried  on  the 
end  of  a  thermal  couple,  and  this  is  connected  to  the  cold 
junction  and  the  galvanometer.  The  readings  of  the  galva- 
nometer and  the  cold  junction,  together  with  the  correction 
plot  of  the  galvanometer,  will  give  the  temperature  of  the 
platinum  from  time  to  time.  If  the  Heraeus  galvanometer, 
with  the  legend  "  Kaiser  and  Schmidt,  Berlin,"  on  the  dial  is 
used,  it  should  be  tapped  lightly  with  the  finger  or  lead 
pencil  before  each  reading  to  eliminate  errors  due  to  pivot 
friction.  The  temperature  of  the  platinum  in  the  furnace 
should  now  be  carried  through  as  wide  a  range  of  tempera- 
ture as  possible,  temperatures  from  650°  C.  to  1500°  C.  being 
easily  maintained  for  a  sufficient  length  of  time  to  make  an 
observation.  Reading  of  the  photometer  should  be  taken  at 
intervals  of  about  100  degrees.  At  least  three  runs  through- 
out the  entire  range  should  be  made.  Since  there  is  but  one 
standard  lamp  provided,  and  we  wish  to  measure  tempera- 
tures through  a  considerable  range,  we  must  have  some 
means  of  making  the  standard  of  greater  or  less  brilliancy 
according  to  the  temperature  range  in  which  the  temperature 
we  are  measuring  lies.  We  do  this  by  inserting  either 
between  the  standard  and  the  eyepiece,  or  between  the  hot 
body  and  the  eyepiece,  an  absorbing  glass  of  a  grayish 
or  smoky  color.  This  alters  the  apparent  intensity  of  the 
object  or  the  standard  in  a  certain  definite  proportion  The 


LE  CH ATELIER  PHOTOMETRIC  PYROMETER        21 

amount  of  the  absorption  is  to  be  obtained  by  taking  readings 
at  some  fixed  temperature  both  with  and  without  the  smoked 
glass.  This  absorption  factor  should  be  determined  with 
the  greatest  care.  All  of  the  pieces  of  glass  are  from  the 
same  sheet  and  have  the  same  absorption  factor,  so  that  only 
one  piece  need  be  examined. 

No  determination  of  the  absorption  factor  need  be  made  if 
we  wish  to  use  the  instrument  over  only  such  ranges  of  tem- 
perature as  those  at  which  we  may  calibrate  ;  but  for  higher 
temperatures  we  must  add  absorbing  glasses  and  correct  the 
apparent  intensities  for  the  amount  absorbed  by  the  glasses. 
For  instance,  suppose  we  have  calibrated  and  gotten  a  plot 
of  the  relation  of  temperature  to  readings  of  the  scale  of 
the  instrument,  or  rather  the  squares  of  the  readings.  It 
will  be  noticed  that  the  scale  indicates  the  amount  of  linear 
movement  of  the  parts  of  the  diaphragm,  and  the  square  of 
the  readings  would  indicate  the  relative  area  of  the  opening 
from  time  to  time  ;  hence  it  is  better  to  plot  the  squares  of  the 
readings  rather  than  the  readings  themselves.  Let  us  then 
take  an  observation  of  the  temperature  of  the  filament  of  one 
of  the  large  incandescent  lamps  used  to  light  the  room.  It 
will  be  found  necessary  to  insert  two  or  three  absorbing  glasses, 
in  order  to  have  a  scale  reading  as  large  as  five  divisions, 
which  is  the  smallest  reading  which  should  ever  be  used,  as 
the  precision  of  smaller  reading  is  very  poor.  Having  gotten 
the  reading  with  three  glass,  for  instance,  if  we  have  only  cali- 
brated with  one  glass  and  without  a  glass,  we  must  reduce 
our  reading  by  extrapolating,  and  should  have  to  assume 
that  the  relation  between  temperature  and  intensity  of  radia- 
tion remains  the  same  at  higher  temperatures.  For  further 
discussion  of  this  the  student  is  referred  to  Le  Chatelier, 
with  the  suggestion  that  until  further  data  can  be  gotten,  it 
is  well  to  use  the  instrument  for  only  such  ranges  as  can  be 
covered  by  a  calibration.  As  an  indicator  of  changes  in 
temperature  it  is,  of  course,  available  over  a  larger  range. 

Each  student,  after  calibrating  and  getting  the  necessary 
data  for  a  plot  of  squared  readings  and  temperatures,  will 
make  determinations  of  the  melting  point  of  copper  and  of 


22         LABORATORY  OF  HEAT  MEASUREMENTS 

one  other  substance,  as  directed  by  the  instructor.  To  do 
this  it  is  best  to  put  one  of  the  small  Fletcher  crucible  fur- 
naces on  the  floor  and  point  the  photometer  down  into  it. 
The  point  where  the  copper  melts  can  be  readily  noted  as  the 
particles  of  oxide  and  slag  begin  to  float  about  on  the  melting 
metal.  Since  all  substances  radiate  at  the  same  temperature 
with  the  same  intensity,  if  only  they  be  enclosed  in  a  recep- 
tacle at  the  same  temperature,  we  may  use  the  surface  of  the 
copper  and  need  not  put  the  piece  of  platinum  into  the 
furnace  near  the  crucible.  If,  however,  the  hot  body  is  not 
in  a  receptacle  at  approximately  its  own  temperature,  the 
platinum  must  be  used. 

The  report  should  include  data  for  the  plot,  the  plot,  and 
the  temperatures  of  the  melting  points  as  deduced  from  the 
plot. 

MESURE    AND    NOUEL    POLARISCOPE 

The  change  in  the  color  of  the  light  coming  from  a  hot 
body  as  its  temperature  changes,  is  the  phenomenon  upon 
which  the  pyrometer  of  Mesure  and  Nouel  is  based.  The 
instrument  is  described  in  detail  in  Le  Chatelier,  page  158. 
It  is  essentially  a  pyroscope  rather  than  a  pyrometer,  be- 
ing useful  for  the  determinations  of  slight  variations  in 


FIG.    6.  —  Mesure   and  Nouel   Polariscope. 

temperature  rather  than  for  the  exact  measurement  of  the 
temperature  itself.  When  a  body  is  heated  it  becomes 
first  red,  then  yellow,  and  finally  white  hot.  In  other 
words,  the  percentage  of  red  light  is  greater  at  the  lower 
temperatures  and  less  as  the  temperature  rises.  The  polari- 
scope,  consisting  of  two  Nicols  prisms  with  a  quarter  wave 
plate  between  them,  serves  to  determine,  at  least  ap- 


MESURE    AND    NOUEL    POLARJSCOPE  23 

proximately,  the  percentage  of  red  in  the  light  from  the 
body  under  examination.  The  relative  position  of  the  two 
Nicols  necessary  to  so  alter  the  light  passing  through  them 
as  to  make  it  of  any  particular  color  is  different  with 
lights  of  different  color,  and  hence  for  light  from  bodies  at 
different  temperature.  For  instance,  with  a  red  quarter 
wave  plate  we  find  it  necessary  to  rotate  the  polarizer  more 
to  cause  the  red  to  disappear  from  the  field  if  the  light 
comes  from  a  very  hot  body  than  if  it  comes  from  one  at  a 
dull  red  heat.  And  this  is  exactly  what  we  do  in  using  this 
instrument.  If  it  be  pointed  at  a  hot  body,  the  field  is  seen 
illuminated  by  a  red  or  a  green  light.  By  turning  the 
polarizer,  the  field  may  be  made  either  red  or  green  as  we 
like,  but  it  will  be  found  that  the  grayish  color  or  "  sensitive 
tint "  which  covers  the  field  when  it  is  just  passing  from  red 
to  green,  or  from  green  to  red,  occurs  at  a  particular  angle 
for  each  particular  temperature  of  the  hot  body.  It  is 
necessary,  therefore,  to  note  the  different  angles  at  which  the 
sensitive  tint  occurs  with  light  from  sources  at  known 
temperatures,  and  then  make  a  calibration  plot.  On  this 
plot  temperatures  may  then  be  found  to  correspond  with 
readings  of  unknown  temperatures. 

Considerable  difficulty  will  be  found  at  first  in  making 
check  readings  with  the  polariscope,  but  patience  and  perse- 
verance will  enable  one  to  make  fair  settings  after  fifteen  or 
twenty  minutes.  If  one  is  color-blind  in  even  the  slightest- 
degree  it  is  impossible  to  use  the  instrument,  with  hope 
of  success,  and  students  whose  eyesight  is  defective  in  this 
way  are  requested  to  notify  the  instructor,  who  will  excuse 
them  from  working  with  this  pyrometer. 

Each  student  will  make  a  partial  calibration  of  the  polari- 
scope and  measure  several  unknown  temperatures.  The 
calibration  is  to  be  made  as  in  the  case  of  the  Le  Chatelier 
photometric  pyrometer  with  the  aid  of  a  bit  of  platinum 
and  the  thermo-electric  pyrometer.  The  temperatures  to  be 
measured  will  be  indicated  by  the  instructor,  if  possible  the 
ordinary  working  temperatures  of  the  small  muffles  and  pot 
furnaces  in  the  mining  laboratory  should  be  among  them. 


24         LABORATORY  OF  HEAT  MEASUREMENTS 

MEASUREMENT   OF    HEAT   OF   COMBUSTION 

There  are  three  methods  of  so  burning  a  fuel  as  to 
measure  its  heat  of  combustion  or  calorific  power :  first,  by 
igniting  it  in  a  stream  of  oxygen ;  second,  by  confining  it  in 
a  strong  receptacle  with  sufficient  oxygen  to  completely  burn 
it ;  and  third,  to  mix  with  it,  before  ignition,  some  solid  which 
will  furnish  oxygen  when  heated.  The  first  method-  gives 
us  the  calorimeters  of  William  Thomson  and  George  Barrus  ; 
the  second,  the  bomb  calorimeter  of  Berthelot,  Mahler,  and 
Norton ;  and  the  third,  the  calorimeter  of  Parr  using  sodium 
peroxide  as  an  oxidizing  substance,  and  that  of  Stohman  and 
Lewis  Thomson  using  chlorate  and  nitrate  of  potassium  or 
peroxide  of  manganese. 

Of  the  several  pieces  of  apparatus  available  for  the 
measurement  of  heat  of  combustion,  all  make  use  of  a 
calorimeter  in  which  to  measure  the  heat  directly.  The 
Junkers  calorimeter,  for  the  measurement  of  the  heat  of 
combustion  of  gaseous  and  liquid  fuels,  is  a  "  continuous " 
calorimeter,  the  others  are  of  the  familiar  "method  of  mix- 
tures "  type.  Of  the  three  methods,  that  making  use  of  the 
bomb  is  most  precise,  that  of  Professor  Parr  is  the  most  con- 
venient and  most  readily  adaptable  to  the  needs  of  engineer- 
ing practice,  while  the  Junkers  apparatus  is  far  better  for 
the  measurement  of  the  efficiency  of  gaseous  fuels  than  any 
of  the  others. 

Coal 

The  coal  from  which  the  sample  is  taken  should  be  free 
from  large  lumps ;  such  lumps  can  be  broken  up  with  a 
hammer. 

After  thoroughly  mixing  the  sample,  spread  it  out  on  a 
piece  of  glazed  paper,  and  take  a  ff  grab  "  or  hand  sample, 
here  and  there,  until  about  75  grams  are  obtained.  If  the 
coal  is  already  finely  ground,  50  grams  will  suffice. 

Grind  this  quantity  in  the  small  iron  mortar  until  it  will 
pass  the  loo-mesh  sieve.  Pass  the  entire  amount  through 
the  screen,  as  otherwise  it  will  have  an  undue  proportion  of 


MEASUREMENT    OF    HEAT    OF    COMBUSTION  25 

the  softer  materials  and  will  not  be  a  representative  sample. 
Pour  the  screened  coal  on  to  glazed  paper,  and,  after  thor- 
oughly mixing,  spread  it  in  an  even  layer  and  sample  with  a 
spatula,  taking  enough  to  nearly  fill  a  wide-mouth  sample 
tube.  Place  this  in  the  drying  closet  at  110°  C.  and  leave 
there  for  fifteen  minutes.  This  heating  is  for  the  purpose 
of  driving  out  the  moisture  so  that  water  will  not  be  weighed 
as  coal. 

Weighing. 

The  balance  used  is  sensitive  to  TV  milligram  and  is 
therefore  delicate  and  must  be  handled  carefully. 

The  arm  is  lowered  on  to  its  knife-edge  by  turning 
the  large  knob  to  the  left,  and  care  must  be  taken  not  to 
do  this  until  approximately  equivalent  weights  are  in  the 
pans. 

Whenever  the  substance  is  removed  from  the  left-hand  pan 
or  the  large  weights  are  changed,  the  balance  arm  must  be 
raised  on  its  supports.  Failure  to  do  this  may  throw  the 
balance  out  of  adjustment  and  permanently  injure  it. 

Fill  a  small  weighing  tube  two-thirds  full  of  the  dry  coal 
and  place  it  on  the  left-hand  pan  of  the  balance.  Weigh  the 
tube  and  coal  to  the  nearest  milligram,  *'.  £.,  the  largest 
division  on  the  arm  of  the  balance. 

After  the  weight  has  been  ascertained,  raise  the  balance 
arm  on  its  supports  and  remove  weights,  corresponding  to 
the  weight  of  coal  desired,  from  the  pan. 

Pour  out  enough  coal,  a  little  at  a  time,  to  counterbalance 
this  change  in  weights  until  within  the  allowable  error  of 
one  milligram. 

Always  record  the  different  weights  of  the  tube  and  coal, 
so  that  the  last  weighing  of  one  sample  may  be  used  as  the 
first  weighing  of  another,  provided  that  no  coal  has  been 
spilled  in  the  meantime. 

In  this  way  several  successive  weighings  can  be  made 
with  rapidity  and  precision.  The  weights  must  be  returned 
to  their  proper  places,  the  balance  arm  raised,  and  the  slide 
closed  after  every  weighing. 


26          LABORATORY  OF  HEAT  MEASUREMENTS 

FUEL   COMBUSTION    BOMB 

The  method  of  measuring  the  heat  of  combustion  of  fuels 
by  burning  them  in  a  bomb  with  oxygen  at  high  pressure 
is  due  to  Berthelot,  and  apparatus  has  been  devised  for 
working  according  to  this  method  by  many  experimenters. 
Perhaps  the  best  known  bombs  are  those  of  Mahler,  Donkin, 
Atwater  and  Hempel.  The  one  used  in  the  Laboratory  of 
Heat  Measurements  is  the  result  of  the  joint  efforts  of  sev- 
eral members  of  the  instructing  staff  of  the  Institute.  It 
differs  from  earlier  bombs  in  material  and  design,  and  the 
result  of  six  years'  use  in  the  hands  of  a  large  number  of 
students  shows  it  to  be  a  durable  as  well  as  a  practical  type 
of  instrument.  It  is  made  of  aluminum-bronze,  having  a 
composition  of  ninety  parts  of  copper  to  ten  parts  of  alumi- 
num. The  object  of  the  use  of  this  particular  alloy  is  to 
avoid  the  lining  with  platinum  or  enamel,  which  has  been 
one  of  tjie  most  troublesome  features  of  many  types  of  bomb. 
This  alloy  is  nearly  or  quite  as  strong  as  steel  and  is  not 
attacked  by  the  oxygen  under  the  ordinary  conditions  of  use. 
The  object  of  having  the  joint  in  the  centre  of  the  bomb 
is  to  insure  ease  of  access  to  all  parts  of  the  inner  surface 
for  cleaning.  The  joint  is  merely  an  enlarged  plumbers' 
union,  and  it  is  essential  that  it  should  be  freely  lubricated 
iipon  the  shoulder  upon  which  the  nut  bears,  but  that  it 
should  be  scrupulously  clean  on  the  bearing  surface  of  the 
lead  -packing  ring.  The  greatest  care  is  needed  to  keep  the 
two  faces  of  the  upper  and  lower  hemispheres  free  from 
scratches  and  dents,  since  otherwise  it  will  be  impossible  to 
make  the  joint  tight.  The  valve  is  essentially  a  delicate 
piece  of  mechanism  and  it  must  not  be  strained. 

The  directions  for  using   the  apparatus  are  given  some- 
what briefly  below. 

The  Bomb. 

Remove  the  calorimeter  from  the  jacket  and    put  into  it 
2,000  c.  c.  of  water  at  a  temperature  of  about  4°  below  that 
of  the  room. 
TOpen  the  bomb  and  put  the  pan  in  place;  cut  off  about 


FUEL    COMBUSTION    BOMB  27 

two  inches  of  the  platinum  fuse  wire  and  connect  it  so  that  it 
passes  from  the  insulated  eye  in  the  bomb,  through  the  hole 
in  the  upright  piece  on  the  pan,  and  across  to  the  other  side 
of  the  pan.  (See  Fig.  7.)  Be  sure  that  the  wire  dips  well 
down  into  the  pan,  but  does  not  touch  the  bottom.  Now  test 
the  fuse  wire  by  touching  one  lead  wire  of  the  igniting  cir- 
cuit to  the  insulated  plug  on  the  outside  of  the  bomb,  and 
the  other  to  the  bomb  itself.  If  the  platinum  wire  flashes 
red,  the  connections  are  properly  made. 


FIG.   7.  —  Combustion  Bomb. 

Weigh  qnejrrarrLof  rpj^  directly  into  the  pan,  and  put  the 
pan  in  position  in  the  bomb.  Having  the  coal  and  fuse  in 
place,  clamp  the  lower  part  of  the  bomb  tightly  in  the  socket 
provided  for  it. 

See  that  the  screw  and  nut  are  scrupulously  clean  and  well 
oiled.  Do  not  put  oil  on  the  lead  packing  ring,  and  see  that 
it  also  is  clean.  Put  on  the  top  half  of  the  bomb,  slip  the 
nut  down  over  it,  and  see  if  it  fits  easily  and  turns  smoothly. 
If  it  does  not,  call  the  instructor. 


o 


28  LABORATORY    OF    HEAT    MEASUREMENTS 

The  bomb  must  be  closed  with  a  strong,  steady  pull,  not  a 
hard  jerk.  Keep  one  foot  well  out  to  the  rear,  to  guard 
against  the  consequences  of  a  slip  of  the  wrench.  Having 
tightened  the  joint,  let  it  stand  for  three  or  four  minutes,  and 
tighten  again  to  take  up  any  looseness  'due  to  the  flowing  of 
the  lead  packing. 

Connect  the  copper  tube  of  the  oxygen  supply  with  the 
nipple  at  the  top  of  the  bomb,  leaving  the  bomb  valve  open  ; 
turn  the  screw  to  the  right  to  open  the  valve,  which  is  "left- 
handed,"  and  be  careful  not  to  strain  this  valve,  as  it  has 
a  very  fine  thread. 

Let  the  oxygen  in  slowly  until  the  gauge  shows  a  pressure 
oijoo  pounds.  Close  both^ valves,  tightly  and  uncouple  the 
tube  from  the  bomb.  Now  put  the  bomb  into  the  calorimeter, 
first  hooking  one  of  the  lead  wires  into  the  ring  in  the  side 
plug  of  the  bomb.  Be  careful  not  to  touch  the  other  lead 
wire  to  the  bomb  while  the  switch  is  closed,  and  thus  prema- 
turely fire  the  charge,  and  also  not  to  move  the  bomb 
violently  enough  to  spill  the  coal  out  of  the  pan. 

Put  the  calorimeter  into  the  water  jacket  and  the  bomb 
into  the  water ;  start  the  stirrer  and  run  five  minutes  before 
the  temperatures  are  read,  as  the  bomb  is  probably  not  at  the 
temperature  of  the  water  when  it  is  first  immersed. 

Insert  the  thermometer  and  read  every  half  minute  for 
fifteen  minutes.  At  the  end  of  the  first  five  minutes,  ask 
instructor  to  ignite  the  charge.  The  temperature  should  rise 
rapidly,  reaching  a  maximum  in  about  two  and  one-half 
minutes,  and  then  fall  slightly  till  the  last  reading  is  made. 
Then  stop  the  motor,  remove  the  bomb  from  the  water  and 
put  back  in  the  clamp. 

%    Open  the  valve  to  let  the  products  of  combustion  escape, 
and  then  open  the  bomb. 

Wash  out  the  pan  and  bomb  and  leave  them  clean  and 
dry. 

The  specific  heat  of  the  bomb  is  .093°;  that  of  the  can 
and  stirrer  is  .095 . 

The  can  and  bomb  can  be  weighed  on  the  platform  scales. 
The  weight  of  the  stirrer  is  100  grams. 


PARR    CALORIMETER  29 

The  cooling  correction  is  to  be  computed  and  allowed  for 
as  directed  in  the  third  year  laboratory  notes  on  heat. 

Each  student  will  make  an  examination  of  two  fuels,  making 
two  combustions  on  each.  The  report  should  give  the  calorific 
power  in  calories  per  gram  and  B.  T.  U.  per  pound  of  fuel. 
Students  must  not  fire  the  charges  until  instructed  specifically 
to  do  so,  as  carelessness  may  result  in  a  serious  explosion. 

PARR   CALORIMETER 

The  calorimeter  for  the  measurement  of  heat  of  combus- 
tion in  which  the  oxygen  is  supplied  from  the  decomposition 
of  sodium  peroxide  is  due  to  Professor  Parr  and  bears  his 
name.  The  essential  parts  of  the  apparatus,  as  shown  in 
Fig.  8,  are  the  combustion  chamber,  the  calorimeter  and 
water  jacket,  and  a  small  motor  to  furnish  power  for  stirring. 
As  originally  planned,  the  ignition  was  to  be  brought  about  by 
dropping  a  hot  wire  through  an  opening  in  the  top  of  the 
combustion  chamber.  This  was  covered  by  a  valve  which 
closed  with  a  spring  when  the  bit  of  hot  wire  had  been 
dropped  in.  Because  of  a  serious  accident  resulting  from 
the  failure  of  the  valve  to  close,  with  consequent  discharge 
of  the  hot  contents  of  the  combustion  chamber  upon  the 
hands  and  faces  of  the  observers,  an  electric  ignitor  has  been 
inserted. 

Setting  up  of  the  Instrument. 

The  calorimeter  should  be  placed  on  a  firm  desk  or  table 
and  accessible  to  motive  power  which  may  come  from  a 
small  electric  motor,  water  motor  or  line  shafting.  The 
power  needed  is  exceedingly  slight,  the  smallest  electric  or 
water  motor  being  ample.  The  speed  when  transmitted  to 
the  instrument  should  not  be  too  high  ;  50  to  100  revolutions 
of  the  pulley  attached  to  the  calorimeter  is  sufficient. 

The  small  rubber  collar  is  to  be  slipped  on  the  stem  of  the 
thermometer,  for  supporting  it  when  passed  through  the 
lid  of  the  calorimeter.  It  should  be  so  placed  as  to  bring 
the  bulb  of  the  thermometer  about  half  way  down  from  the 
top  of  the  can.  While  other  preparations  are  progressing, 


3O         LABORATORY  OF  HEAT  MEASUREMENTS 

hang  the  thermometer  near  the  calorimeter,  in  order  to  ascer- 
tain the  temperature  of  the  room. 

Fill  the  two-liter  flask  to  the  mark  with  water  about  4° 
below  the  room  temperature.  The  calorimeter  should  be 
removed  from  the  instrument  for  filling.  Inside  of  the  calori- 
meter should  be  placed  the  deflecting  collar  and  pivot.  The 
combustion  chamber  should  be  -perfectly  dry  inside  and  out. 

To  prepare  the  combustion  chamber  for  filling,  screw  on 
the  bottom  firmly,  so  as  to  avoid  any  possibility  of  admitting 


FIG.    8.  —  Parr  Fuel  Calorimeter. 


water  to  the  interior,  then  place  it  on  a  sheet  of  white  paper. 

The  sodium  peroxide  and  the  small  measuring  cup  are  to 
be  kept  in  a  glass  jar,  which  must  be  kept  closed.  The 
sodium  peroxide  must  not  be  scattered  about,  and  care  should 
be  taken  not  to  get  it  upon  the  clothes  or  hands.  Keep 
everything  with  which  the  sodium  peroxide  comes  in  contact 
perfectly  dry. 

The  directions  for  manipulation  follow.  After  the  final 
reading  in  a  test  has  been  taken,  dismantle  by  first  carefully 
removing  and  hanging  up  the  thermometer.  After  removing 


PARR    CALORIMETER  31 

the  pulley  and  cover,  take  out  the  calorimeter  entire,  then 
remove  the  cartridge  from  the  water,  remove  the  spring  clips 
with  vanes,  unscrew  the  ends,  clean  them  at  once  with  a  dry 
towel,  and  place  the  cartridge  under  the  tap  or  in  a  basin  of 
water.  The  contents  should  dissolve  out  rapidly  and  in  a 
few  minutes  the  cartridge  will  be  ready  for  rinsing  and 
drying.  Dissolving  the  contents  of  the  cartridge  in  a  basin 
has  the  advantage  of  indicating  whether  the  combustion  i,s 
perfect  or  not.  Of  course  precipitated  iron  and  ash  will 
always  be  in  evidence.  The  result  is  still  better  shown  by 
acidifying  with  commercial  hydrochloric  acid,  when  practi- 
cally a  clear  solution  should  result. 

Manipulation. 

The  coal,  properly  sampled,  should  be  ground  in  a  mortar 
and  passed  through  a  loo-mesh  sieve.  The  amount  so 
treated  need  not  be  large,  an  ounce  or  less  being  sufficient. 
Upon  a  carefully  counterpoised  watch-glass  weigh  exactly 
one-half  gram  and  place  in  the  oven  to  dry.  The  oven 
should  be  maintained  at  105°  to  no0  C.  The  coal  will 
be  sufficiently  dry  in  fifteen  minutes,  having  been  dried 
previously.  If,  however,  an  accurate  determination  of  the 
water  is  desired,  it  should  remain  in  the  oven  at  the  above 
temperature  for  one  hour  and  cooled  in  a  desiccator  or  in 
ground-clamped  watch-glasses  before  weighing  the  second 
time.  For  the  calorific  test  the  determination  of  the  water  is 
not  necessary,  hence,  after  fifteen  minutes  in  the  oven  at  the 
proper  temperature,  the  sample  is  ready.  Students  need  not 
take  time  for  this.  To  the  half  gram  of  coal,  when  cooled  to 
about  the  temperature  of  the  hand,  add  in  the  watch-glass  or 
upon  a  piece  of  glazed  paper,  one  measure  —  the  small 
dipper-like  measure  in  the  glass  jar  —  of  sodium  peroxide. 
Mix  thoroughly  and  carefully  with  a  knife  or  spatula.  Do 
not  grind  the  mixture,  but  turn  it  and  stir  it,  and  be  as  quick 
as  possible.  Put  the  entire  mixture  into  the  combustion 
chamber.  See  that  the  bottom  is  screwed  on  firmly  before 
filling,  and  put  the  fine  platinum  fuse  in  place  between  the 


32         LABORATORY  OF  HEAT  MEASUREMENTS 

brass  posts  on  the  under  side  of  the  cover.  It  is  well  to 
put  the  chamber  on  a  piece  of  blue  glazed  paper  so  that  par- 
ticles which  are  spilled  may  readily  be  collected. 

The  measure  is  adjusted  to  hold  very  nearly  8^  or  9  grams 
of  sodium  peroxide  when  tapped  to  settle  the  contents,  and  at 
the  same  time  shake  off  the  excess  at  the  top  so  that  it  will  con- 
form somewhat  to  a  "  struck"  measure.  Extreme  accuracy 
m  this  regard  is  not  essential.  Be  sure,  however,  that  the 
measure  has  been  filled  to  the  exclusion  of  large  cavities  that 
may  tend  to  form.  Return  the  measure  to  the  glass  jar  at 
once,  and  keep  the  whole  covered  and  clamped  to  exclude 
moisture. 

When  the  mixing  is  complete,  tap  the  cartridge  lightly  on 
the  bottom  to  settle  the  contents  and  to  shake  all  the  material 
from  the  upper  part  of  the  cylinder.  Put  on  the  spring  clips 
with  vanes.  The  cartridge  is  now  ready  for  inserting  in  the 
calorimeter.  The  calorimeter  is  made  ready  by  standing  it 
outside  the  apparatus  and  adding  thereto  2,000  cubic  centi- 
meters of  distilled  water  which  has  been  previously  brought 
to  a  temperature  a  little  below  that  of  the  room, — say  about 
4°  C.  This  adjustment  of  the  temperature  of  the  water 
should  be  made  while  it  is  yet  in  the  two-liter  flask.  If  too 
warm,  allow  the  tap  water  to  flow  over  the  flask.  If  too  cold, 
pour  a  little  into  a  beaker  and  heat  over  a  Bunsen  burner, 
or  better  still,  if  available,  hold  the  flask  under  a  hot  water 
faucet.  Mix  the  water  in  the  flask  before  thus  roughly 
taking  the  temperature.  Since  the  average  coal  gives  a 
total  rise  of  about  3°  C.  for  \  gram,  it  is  a  simple  matter  to 
know  approximately  what  the  initial  temperature  of  the 
water  should  be.  It  is  well  to  make  a  note  of  the  tempera- 
ture of  the  room  in  the  data  of  the  experiment. 

Pour  the  water  into  the  calorimeter  and  lift  the  same  into 
the  jacket.  The  pouring  in  of  the  water  should  be  made 
with  the  calorimeter  removed,  to  avoid  getting  any  moisture 
on  the  outside  of  the  calorimeter  or  in  the  air  spaces.  Now 
insert  the  combustion  chamber,  adjust  the  cover,  place  the 
thermometer  so  the  bulb  will  extend  about  half  way  to  the 
bottom  of  the  calorimeter,  place  the  pulley  on  the  stem, 


PARR    CALORIMETER  33 

adjust  the  arm  carrying  the  igniting  brushes,  and  connect  with 
the  motor.  The  general  arrangement  of  parts  is  shown  in 
Fig.  7.  Too  rapid  revolving  of  the  cartridge  should  be 
avoided,  50  to  100  revolutions  per  minute  being  sufficient. 
The  cartridge  should  turn  to  the  right,  or  as  the  hands  of  a 
watch,  thus  deflecting  the  water  currents  downward.  Read 
the  thermometer  carefully  every  fifteen  seconds.  After  five 
minutes  ignite  the  charge  by  closing  the  switch.  The  com- 
bustion should  be  indicated  by  a  rapid  rise  of  the  mercury, 
which  reaches  its  maximum  height  after  about  five  minutes. 
Read  the  thermometer  every  fifteen  seconds  to  the  nearest 
ifa°  until  ten  minutes  after  it  starts  to  rise.  Make  note  of 
the  final  maximum  temperature  and  compute  as  follows : 
The  cooling  connection  should  be  made  as  indicated  in  the 
Laboratory  Notes  on  Heat  in  use  in  the  third-year  labora- 
tory, and  if  it  is  so  small  as  to  be  negligible,  it  should  be  so 
stated  in  the  report. 

The  difference  is  the  actual  rise  "  r  "  due  to  the  total  reac- 
tion inside  of  the  cartridge.  Multiply  "r"  by  the  factor 
3,100  and  the  product  equals  the  calories  per  gram  of 
coal. 

Notes.  —  (a)  The  factor  3,100  is  deduced  as  follows; 
The  water  used  plus  the  water  equivalent  of  the  metal 
in  the  instrument  amounts  to  2,123  grams.  In  the  reac- 
tion, 73  per  cent,  of  the  heat  is  due  to  combustion  of  the 
coal,  and  27  per  cent,  is  due  to  the  heat  of  combination  of 
CO»  and  HO,,  with  the  sodium  peroxide  and  monoxide. 

If  now  \  gram  of  coal  causes  2,123  grams  of  water  to 
rise  "r"  degrees,  and  if  only  73  per  cent,  of  this  is  due  to 
combustion,  then  — 

.73  X  2123  x  2  x  f V"  =  heat  that  results  from  the  com- 
bustion of  one  gram  of  coal.  2  =  3100.00  x  "  r" 

Give  the  calorific  power  in  B.  T.  U.  per  pound  as  well  as 
in  calories  per  gram. 

(b)  The  moisture  in  "  air  dry  "  coal  may  vary  from  one  to 
fifteen  or  more  per  cent.  When  this  quantity  does  not 
exceed  two  or  three  per  cent.,  the  error  introduced  in  the 
reaction  by  not  removing  it  would  be  too  small  to  be  of  tech- 


34         LABORATORY  OF  HEAT  MEASUREMENTS 

nical  consequence.     It  is  better,  however,  in  all  cases  to  dry 
the  coal  as  directed. 

(c)  In  the  case  of  coke,  drying  is  usually  unnecessary. 
Ashes,  if  they  have  been  sprinkled,  should  of  course  be  dried. 
Ashes  and  sometimes  coke  ignite  with  difficulty.     In   such 
cases  add  a  second  charge  of  sodium  peroxide  and  %  gram 
of  some  good  coal,  the  ijactor  of  which  has  been  determined, 
mix  the  two  charges  thoroughly  by  shaking,  and  ignite.     The 
coal   will  carry  along   the  combustion    of   the    entire   mass. 
Calculate  the  B.  T.  U.  as  usual  and  substract  the  B.  T.  U. 
due  to  the  coal. 

( d)  The  receptacle  for  the  sodium  peroxide  is  so  arranged 
that,  with  the  contents  of  one  can  of  sodium  peroxide  in  the 
bottom,  there  is  still  room  in  the  jar  for  the  measure  .and 
handle  complete.     The  measure  should  always  be  replaced 
in  the  jar  and  the  cover  clamped  on. 

(tf)  Do  not  spill  the  sodium  peroxide.  Do  not  pour  a 
mixture  of  the  sodium  peroxide  and  coal  into  water.  It  may 
ignite  violently.  When  thrown  into  wet  excelsior  or  damp 
organic  matter  may  cause  ignition.  If  much  is  spilled  on 
the  hands  wash  thoroughly  at  once.  The  fine  dust  that  may 
be  breathed  into  the  nostrils  is  harmless ;  use  care  and  com- 
mon sense.  There  should  be  no  more  liability  to  accident 
than  in  the  use  of  any  other  caustic. 

(y*)  A  sample  of  coal  ground  finely,  even  if  carefully 
kept  in  a  corked  bottle,  slowly  deteriorates.  An  appreciable 
loss  may  be  noticed  after  a  week.  As  much  as  two  per  cent, 
deterioration  has  been  noted  after  six  or  eight  weeks.  Lump 
or  pea  samples  are  not  thus  affected. 

JUNKERS    GAS    CALORIMETER 

The  Junkers  calorimeter  is  available  for  the  measurement 
of  the  heat  of  combustion,  or  calorific  power  of  gas,  kero- 
'sene,  and  gasoline.  The  apparatus  is  illustrated  in  the 
accompanying  cuts.  The  calorimeter  is  of  the  "continuous" 
type.  It  is  essentially  a  small  tubular  boiler  in  an  upright 
position.  The  heat  developed  by  the  flame  under  the  boiler 


JUNKERS    GAS    CALORIMETER 


35 


raises  the  temperature  of  the  water  as  it  passes  through 
the  apparatus.  A  measurement  of  the  amount  of  water 
passing,  and  the  amount  of  the  temperature  rise,  gives  us 
at  once  the  heat  developed  by  the  flame.  This  may  be 
expressed  in  calories,  o*  gram-degree  C.  units  or  in  British 
Thermal  Units,  the  pound  degree  F.  unit. 

To  set  up  the  apparatus  it  is  first  necessary  to  so  locate 
the  boiler  that  it  may  have  a  constant  supply  of  water  at  a 
nearly  constant  temperature.  If  there  are  great  fluctuations 


FIG.    9.  — Junkers  Gas  Calorimeter. 

of  the  temperature  of  the  supply  mains,  a  large  tank  at  the  top 
of  the  room  will  answer  for  several  determinations.  If  it  can 
be  fitted  with  a  ball  cock,  as  are  the  common  tanks  for  house- 
hold hot  water  supply,  it  will  serve  admirably.  Beside  con- 
stant temperature  of  the  water  supply  one  other  condition 
must  be  maintained,  — that  of  constant  "  head  "  or  pressure. 
This  is  accomplished  by  means  of  the  small  cup,  which  is  to 
be  kept  full  while  the  apparatus  is  being  used.  The  best*way 
to  be  sure  that  the  cup  is  full  is  to  keep  the  overflow  pipe 
dripping  slightly.  It  is  well  to  put  this  in  a  conspicuous  place 
so  that  a  stopping  of  the  overflow  may  be  immediately  noted 
and  more  water  supplied  to  the  cup.  The  outlet  pipe  should 


36         LABORATORY  OF  HEAT  MEASUREMENTS 

be  provided  with  a  three-way-cock  connection,  so  that  the 
water  which  has  passed  through  the  calorimeter  may  be  run 
into  the  tank,  to  be  weighed  or  measured,  or  into  the  drain 
as  desired.  It  is  necessary  to  so  arrange  this  that  the  transfer 
from  tank  to  drain  may  be  made  quickly,  as  we  wish  to 
begin  the  measurement  of  the  water  at  a  definite  time  with  a 
precision  of  about  one  second.  The  water  may  be  measured 
in  calibrated  flasks,  but  it  is  much  better  to  weigh  it  and  to 
use  a  long  run  and  a  large  amount  of  water. 


The  gas  meter  for  use  with  this  experiment  may  be 
assumed  to  be  in  proper  order  without  calibration  correction. 
If,  for  any  reason,  the  meter  is  jarred  or  moved,  it  must  be 
emptied  and  refilled.  The  dial  reads  in  liters,  being  gradu- 
ated so  that  one  revolution  of  the  long  pointer  indicates  three 
liters.  The  small  dial  has  divisions  of  three  liters,  making 
one  revolution  on  the  large  dial  correspond  to  one  division  on 
'the  smaller  dial.  The  pressure  regulator  must  be  put  in  the 
pipe  from  the  meter  to  the  calorimeter.  It  is  a  floating 
inverted  cup  which,  as  it  fills  with  gas  and  rises  in  the  water, 
closes  the  valve  through  which  it  filled  and  then  falls,  to  be 
filled  again.  The  pressure  of  the  gas  coming  from  it  may 
be  regulated  by  adjusting  weights  on  the  top  of  the  cup, 
changing  its  tendency  to  sink,  and  the  length  of  time  for 
which  the  valve  remains  open.  The  regulator  should  be 
filled  with  water  to  a  depth  of  about  three  inches.  If  gaso- 
line or  oil  are  to  be  tested  instead  of  gas,  it  is,  of  course,  not 
necessary  to  use  either  meter  or  regulator,  but  the  lamp 
should  be  put  under  the  calorimeter  on  platform  scales,  and 
the  loss  of  weight  as  the  lamp  burns  should  be  noted  and 
recorded  just  as  are  the  gas  meter  readings  in  the  determi- 
nation under  discussion.  Having  gotten  the  meter  setup,  the 


JUNKERS    GAS    CALORIMETER  37 

regulator  filled  and  in  position,  the  calorimeter  filled  and  the 
supply  cup  overflowing,  the  burner  must  be  removed  and 
lighted  and  then  clamped  in  position  under  the  central  tube 
of  the  calorimeter.  The  temperature  of  the  outlet  water 
should  at  once  rise.  Watch  it  carefully  for  several  minutes 
to  see  that  it  does  not  go  high  enough  to  endanger  the 
thermometer.  It  should  be  regulated  in  height  by  changing 
(the  amount  of  water  entering  the  apparatus  by  means  of  the 
valve,  which,  with  its  dial,  affords  a  very  clos'e  adjustment. 
It  is  well  to  adjust  the  supply  so  as  to  have  the  difference 
between  the  inlet  and  outlet  temperatures  about  fifteen  degrees. 
Be  careful  never  to  start  the  fire  under  the  boiler  unless  you 
are  certain  that  it  has  its  normal  amount  of  water. 

No  observation  should  be  taken  after  the  adjustment  of  the 
water  supply  unti,l  after  an  interval  of  five  minutes,  in  which 
the  whole  calorimeter  may  come  to  a  condition  of  equilibrium. 
The  necessity  of  the  delay  in  starting  lies  in  the  slowness 
with  which  the  condensed  water  begins  to  drip  at  a  steady 
rate.  Observations  taken  within  five  minutes  of  the  read- 
justment of  the  gas  supply  are  liable  to  be  in  error*  because 
of  this  slowness  or  "lag"  in  the  drip,  by  several  per  cent. 
The  observations  to  be  taken  are  the  temperature  of  the  inlet 
and  outlet  water,  the  amount  of  gas  or  oil,  and  the  weight 
of  water  passing  per  minute.  It  is  well  to  make  a  run  of 
eight  minutes' duration.  The  gas  meter  should  be  reacPat 
the  beginning  of  the  run  and  once  each  minute  during  the 
run,  so  that  the  rate  of  gas  supply  per  minute  may  be  known. 
The  weighing  of  the  water  should  be  begun  at  a  carefully 
npted  time,  preferably  the  time  at  which  the  gas  meter 
readings  are  begun,  and  ended  at  the  close  of  the  stated 
eight  minutes  with  a  precision  of  one  or  two  seconds.  If,  in 
an  eight-minute  run,  we  are  in  doubt  as  to  the  length  of  time 
taken  by  the  gas  or  water  which  has  been  measured,  in 
passing  through  the  calorimeter,  by  an  amount  as  gre*at  as 
two  seconds  we  are  in  doubt  as  to  the  calorific  power  of  the 
gas  by  about  two  parts  in  480,  or  nearly  one  half  of  one  per 
cent.  This  will  emphasize  the  necessity  of  making  a  long 
run.  The  thermometers  may  be  read  at  such  times  as  are 


38         LABORATORY  OF  HEAT  MEASUREMENTS 

convenient  without  disturbing  the  gas  meter  readings,  but 
at  intervals  not  longer  than  thirty  seconds.  The  drip  from 
the  condensed  gas  is  to  be  collected  for  the  entire  run. 
We  should  have  at  the  close  of  the  run  the  following 
observations  :  — 

L  Table  of  inlet  temperatures  (30  seconds). 
^  Table  of  outlet  temperatures  (30  seconds). 
v  Table  of  gas  meter  readings   (Start,  minute  intervals  to 
finish). 

Weight  of  water  passing  in  entire  run. 
Weight  of  drip,  for  entire  run. 
«•  Time  of  start  and  finish. 

The  formula  necessary  for  the  reduction  of  these  observa- 
tions is  as  follows  :  — 

Let      W  =  grams  of  water  passing  per  minute. 
/  =  average  temperature  of  inlet  water. 
T=  average  temperature  of  outlet  water. 
G  =  liters  of  gas  burned  per  minute. 
d  =  grams  of  water  condensed  per  minute. 
H  '  =  heat  of  combustion  of  one  liter  of  gas  in  calories. 

Then: 


G 


The  calorimeter  measures  directly  without  allowing  for 
the  drip  the  total  heat  of  combustion  of  the  gas,  but  since 
few  heating  devices  condense  the  water  in  the  products  of 
combustion,  but  allow  the  water  to  escape  as  steam,  it  is  nec- 
essary to  report  for  commercial  tests,  not  only  upon  the 
total  calorific  power  of  the  gas,  but  also  upon  its  calorific 
power  when  used  in  a  gas  engine  or  gas  heater.  To 
do  this  it  is  necessary  to  collect  the  drip  and  to  subtract 
its  latent  heat  of  condensation  from  the  total  heat  as  measured 
by  the  calorimeter.  Since  the  latent  heat  developed  by  one 
gram  of  water  in  condensing  is  537  calories,  it  is  necessary 
to  multiply  the  weight  in  grams  by  537,  as  indicated  by  the 
last  term  of  the  equation  above. 


JUNKERS    GAS    CALORIMETER  39 

Report.  —  Each  pair  of  students  will  make  three  determi- 
nations of  the  calorific  power  of  the  Boston  city  gas.  Use 
slightly  different  rates  of  gas  by  changing  weights  on  pressure 
gauge.  Make  also  a  duplicate  set  of  determinations  of  the 
calorific -power  of  kerosene,  burnt  in  an  ordinary  lamp  and 
in  a  blue-flame  lamp,  and  of  gasoline  in  the  Barthel  lanv^. 
Report  on  the  gas  in  calories  per  litre  and  also  in  B.  T.  IL 
per  cubic  foot.  The  liquid  fuels  are  to  be  reported  in  calories 
per  gram  and  B.  T.  U.  per  pound.  Leave  the  apparatus 
with  both  water  and  gas  supply  cut  off,  and  the  oil  and 
gasoline  burners  returned  to  their  proper  places. 


.     OF  THE     " 


\OQec 


.'51 EB 


I  U      I   I 


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